Transmission control



Nov. 3, 1942. E. l. GREEN TRANSMISSION CONTROL Filed April 26, 1941 2 Sheets-Sheet 1 mmf Imm'

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/Nl/ENTOR E GREEN BV Patented ov. 3, 1942 2,300,415' TRANSMISSION cN'rnoL Estill I. Green, Short Hills, N. J., assigner to Bell Telephone York, N. Y.,

7 Claims.

This invention relates to transmission systems utilizing a Wide band of frequencies and more particularly to regulation of the transmission characteristics of repeaters in such systems to compensate for changes in the transmission properties of the transmission medium. l

A principal object of the inventionis to improve and simplify the construction and operation of transmission regulating equipment for wide band signaling systems.

Another and more particular object is to provide a simple and economical arrangement for automatically regulating the transmission characteristics of repeaters in a signaling system to compensate automatically for changes in the transmission characteristics of the transmission medium that are non-uniform over the frequency range occupied by signals.

Although the present invention will be described hereinafter largely in terms of its application to the control of repeater gain in a wide band Wire line signaling system, -it will become apparent that the invention, at least in its broader aspects, is not limited in these respects and that it is susceptible of various other embodiments within the spirit and scope of the appended claims.

It is well known that in long distance wire line signaling systems, the attenuation of the line varies over a wide range with changes in temperature and other` eects, and that it is desirable to eiect compensating changes in the system to maintain the transmission equivalent thereof substantially constant. One method of automatic compensation proposed heretofore involves the transmission concurrently with the signals of a single frequency pilot wave that experiences the same attenuation as the signals, and automatic regulation of the gain of the signal repeaters in the System under the control of the pilot wave. The compensating gain change thus introduced is a flat gain change, that is, it is the Same at all frequencies in the signal frequency rangie. The' line attenuation change, however, is ordinarily not quite the same at all frequencies and in a long distance wide band system it may be desirable to supplement the fiat gain regulation with a compensating gain change that is not uniform over the frequency range. To a first approximation the non-uniform gain change required is a change in the slope of the gain-frequency characteristic of the repeater.

For automatic slope control it has been proposed that a predetermined change of slope be introduced in accordance with the change in am- Laboratories, Incorporated, New a. corporation of New York Application April 26,

1941, Serlal No.- 390,471

(Cl. 179-15) l plitude of a single pilot frequency. This method is not entirely satisfactory since a given change of pilot level may involve a fairly wide range of different slopes. It has also been proposed that two pilot waves of different frequencies be transmitted concurrently with the signals so that at the repeater stations a measure can be had of the difference in line attenuation at the two frequencies. Changes in the relative intensities of the two pilots indicate changes in the slope characteristic of the transmission line and they may be utilized to effect automatically a compensating change in the slopecharacteristic of the -repeaters. This automatic slope regulation requires at least one additional pilot frequency in each direction of transmission.

In accordance with a feature of the present invention automatic slope regulation is provided without the addition of pilots other than lthose required and used for fiat gain regulation.

In accordance with another feature of the present invention, individual pilot channels respectively associated with a pluralityv of transmission systems superposed on the same transmission line or medium are conjointly utilized to effect non-uniform repeater gain control in one or more of the superposed systems in addition to eiecting uniform or fiat gain control in their respective systems.

In accordance with still another feature of the invention, pilot currents of different frequencies transmitted in opposite directions through a transmission line or other medium for at or uniform gain control of individual, oppositely directed systems are utilized jointly to effect nonuniform gain control or, more specifically, slope control of one or more of the superposed systems and for either one or both directions of transmission therein.

'I'he nature of the present invention and its various features, objects and advantages will appear more fully from a consideration of the em- Cab bodiments illustrated in the accompanying drawings, in which:

Fig. 1 shows the invention as embodied in a multiplex signaling System utilizing two oppositely directed pilots for controlling flat gain in each direction of transmission; and

Fig. 2 shows an embodiment of the invention utilizing like-directed pilots of different frequencies that are used to regulate the flat gain characteristics of two superposed multiplex telephone systems.

Referring more. particularly now to Fig. 1,

there are shown two successive repeater stations in a multiplex transmission system embodying the present invention. In general outline, there is provided a two-way voice frequency telephone system and a two-way multiplex carrier telephone system superposed on the same pair of line conductors. In the carrier telephone portion of the system, one group of channels is utilized for multiplex transmission in one direction through the system and another group of channels in a different frequency range is utilized for multiplex transmission in the opposite direction, With each of these two groups of channels there is associated an individual pilot wave transmitted concurrently with the signals for effecting automatic fiat gain control in the repeater amplifiers.

The two repeaters stations shown are or may be exactly alike and there may be, for example, many other stations of the same kind spaced apart in the transmission line connecting the terminals of the system as well is other repeater stations equipped for only fiat gain regulation or for none at all.

As will appear from a consideration of station the voice frequency system is provided with a 22-type repeater that is connected into the transmission line L through low-pass filters 5. In parallel with the voice frequency repeater but effec tively isolated therefrom by high-pass filters 6 is a repeater for the superposed carrier system. In the carrier repeater, the W-E amplifier section is isolated by directional filters 1 and I2 at the input and output respectively thereof, these filters passing only the W-E group of carrier telephone channels and its associated fiat gain controlling pilot wave. The E--W section is similarly equipped with directional lters 51 and 62.

It may be supposed for specific example that the W-E carrier channels are three in number and occupy the frequency range from 17.7 to 28.4 kilocycles and that the frequency JI of the accompanying pilot wave is 24.4 kilocycles. Similarly the E-W group of carrier channels may also be three in number and occupy the frequency range from 6.3 to 15.8 kilocycles, the frequency f2 of the respectively corresponding pilot wave being 9.4 kilocycles.

Examining the W--E section of the carrier repeater at station I, the directional input filter 1 thereof is followed by an amplifier 8', a variable equalizer 9, a variable attenuator I0, an amplifier and the directional output filter I2. At the output of amplifier pilot fl` is partially divverted through a filter I4 and the amplitude variations thereof are utilized in control circuit I5 to so adjust variable attenuator I0 as to maintain the pilot level at the output of amplifier |I substantially constant. Flat gain regulators appropriate for this portion of the circuit are well known in the art.

The E-W section of the carrier repeater is substantially the same as the W-E section excepting for the frequency range to be accommodated, and elements 51, 58, etc., thereof respectively correspond with elements 1, 8, etc. It will be understood then that pilot f2 in the E-W section operates on variable attentuator 60 to control the fiat gain in the E-W direction and to maintain the output intensity of pilot ,f2 substantially constant. The same is true at repeater station 2 where elements |01, |08, etc., are respectively the same as elements 1, 8, etc., and elements respectively the same as elements 51, 58, etc., may be readily identified.

Considering briefiy the transmission between the two repeater stations, it will be evident that the amplitude of pilot 1| as received at station 2 affords a measure of the line attenuation at frequency l I and that changes in the received pilot amplitude indicate directly the extent and direction of changes in line attenuation at frequency fl. Likewise the amplitude of pilot f2 as received at station I affords a measure'of the line attenuation at its frequency and changes in its amplitude indicate directly the extent and direction of changes in line attenuation at frequency f2. As previously described, these changes in pilot amplitudes are utilized at the respective .stations at which they are observed to effect a compensating change in the flat gain of the repeater.

In accordance with a principal feature of the present invention, the two pilots fl and f2, provided for regulating the fiat gain in the respective directions of transmission, are utilized without the aid of additional pilots to effect slope control of the several repeater gain characteristics. 'I'he specific means provided for this purpose are as follows.

At the input of amplifier |08 in station 2, the pilot fl is partially diyerted through a filter IIB, amplified and applied to a rectifier ||1. The unidirectional output current from rectifier ||1 is then applied through a motor-controlled voltage divider IIB-IIS to one winding |2| of a differentialrelay |20. Likewise, at the input of amplifier 58 in station I, the pilot f2 is partially diverted through a filter 66, amplified and applied to a rectifier 61, the output of which is connected through a motor-controlled voltage divider 68-69 to one winding 1| of a differential relay 10` Composite sets 4 and |03 at the terminals of the intervening section of line L provide two ground-return circuits each utilizing one of the line conductors and each appropriate for the transmission of unidirectional currents. One of these ground-return circuits is connected to the output terminals of rectifier 61 and the other end thereof is connected at station 2 to a winding |22 on differential relay |20. Inesmuch as the output of rectifier 61 fluctuates in accordance with the varying intensity of pilot f2 as received at station I, the unidirectional current in relay windings |22 varies likewise, for the line attenuation is substantially constant for dlrect current.

Thus at station 2, the armature |23 of, differential relay |20 is subject to the opposing effects of the respective currents in windings |2l and |22, the one effect tending to be proportional to the intensity of the pilot fl as received at station 2 and the other tending to be proportional to the intensity of pilot f2 as received at station I. Relay armature |23 is connected in the control circuit of motor |24 which in turn controls simultaneously the position of the contactor ||8 on voltage dividing resistor H8 and the slope of the attentuation characteristic introduced by variable equalizer |09. If the opposing effects in relay |20 are equal, armature |23 assumes a neutral position. If they are unequal the armature is moved in one direction or the other, depending on which effect is the greater, to cause motor |24 to rotate in such direction that the consequent movement of contactor IIS is in the proper direction to bring the opposing forces to equality.

The difference in intensity of the two pilots. as received at the respective repeater stations after transmission over the intervening section of line L, is correlated with the slope characteristic d! the line attenuation, and changes in the intensity differential aord a direct measure of slope changes in line attenuation. Inasmuch as the position of contactor ||9 is uniquely correlated with the intensity differential, it follows that for every position of the contactor there is a definite change in slope characteristic to be introduced by equalizer |09. The latter can be and is so varied concurrently with the movement of contactor ||9 as to introduce the required compensating change in repeater slope characteristic.

Whereas automatic slope regulation is thus provided in the W--E path at station 2 to compensate for the varying slope characteristic of the intervening section of transmission line L`,'sta tion I is similarly equipped to provide automatic slope regulation for E-W transmission through the same line section. More particularly the other ground-return circuit afforded by composite sets 4 and |03 is utilized to convey from the output of rectifier to Winding 'l2 on relay 10 a measure of the intensity of pilot .fl as received at station 2. This measure is compared at station .l with the output of rectifier El and the intensity dierential is utilizedl to control motor 14 and voltage divider 68-89 and to continuously maintain a balanced condition. Motor 14 simultaneously controls the changes in slope characteristic that variable equalizer 59 introduces in the E-W signaling path at station It will be understood too that differential relay 20 at station and differential `relay |10 at station 2 together with their associated control equipment cooperate with similar apparatus at other repeaters to compensate the changing slope characteristics of the adjoining sections of transmission line.

Fig. 2 illustrates schematically one of a succession of identical repeaters embodying the present invention in a form somewhat different from that described with reference to Fig. 1. In this embodiment twoseparate two-way multiplex carrier telephone systems and a two-.way voice frequency telephone system are superposed in muliplex carrier relation on the same transmission line. Carrier system No. 1 may be the same as the carrier system described with reference to Fig. 1 excepting for the means provided for automatic regulation of the slope characteristic ofV the repeaters. It is so illustrated and corresponding elements are identified by the same reference characters. Carrier system No. 2 may be a twelve-channel system, for specific example, occupying the frequency range from 36 to 140 kilocycles. At the repeater station this second carrier system is isolated .by high-pass line filters 205 and 201 for application to a repeater. Low-pass line lters 205 and 208 similarly segregate the other carrier system and the voice frequency system which in turn are separated from each other by low-pass and high-pass lters and 6.

In carrier system No. 1 a pilot wave fl of 24.4 kilocycles, for example, accompanies the signals in the W-E direction of transmission and, as before, is utilized to adjust variable attenuator |0 and thereby effect automatic at gain regulation. Likewise a pilot wave f2 of frequency 9.4 kilocycles accompanies the E-W channels in carrier system No. 1 and is utilized as before to control the flat gain adjustment at variable attenuator 50.

In carrier system No. 2 a pilot wave f3 of frequency 59.9 kilocycles, for example, is transmitted concurrently with the signals in the W-E direction of transmission, and a pilot Wave f4 of frequency 116.1 kilocycles, for example, is similarly transmitted with the signals in the E-W direction. These two pilots control the fiat gain in the respectively corresponding portions of the system No. 2 repeater. Excepting as it is adapted for a dilerent frequency range, this repeater is or may be the sa-me as the repeater for carrier system No. 1, and the two pilots f3 and f4 are similarly used for regulating the fiat gain therein. Thus at the output of the W-E repeater section pilot f3 is diverted through lter 2|4 and applied through control circuit 2|5 to the dat gain regulator, i. e., variable attenuator 2|0. Similarly at the output of the E-W repeater section pilot f4 is diverted through filter 264 and utilized to effect automatic flat gain regulation by controlling the loss introduced by variable attenuator 260.

.Whereas Fig. 2, as hereinbefore described, provides only the minimum number of pilot waves necessary for automatic dat gain regulation in the two superposed carrier systems, automatic slope regulation for both systems and for both directions of transmission is derived in accordance with the invention without the addition of other pilot waves. In general, pilot .waves fl and f3 are utilized to control motor 24 to effect automatic slope adjustment of variable equalizers 9 and 209 in -the W-E paths olf the respective carrier systems. Similarly, pilot waves f2 and f4 jointly control motor 214 to eiect automatic slope adjustment of variable equalizers 59 and 259 in the E-W paths.

Considering first the means provided for slope regulation in the W-E direction of transmission,

it will be noted that the respective amplitudes of pilot waves f| and f3 as received at the repeater station afford an indication of the line equivalen-t or attenuation at the frequencies of the respective pilots. The difference in lattenuation at these.

Itwo frequencies aords a measure of the slope characteristic of the transmission line and may be utilized to effect a :compensating adjustment in the slope characteristic of the repeater.

Thus at the respective inputs of the W-E sections of the two repeaters the two pilot waves fl and f3 are picked 01T I6 and 2| 6, amplified and applied to the respective rectiers I1 and 2|'|. The output of rectifier is applied through motor controlled voltage divider |8|9 to one winding 2| of differential relay 20. 'I'he output of rectifier 2|'| is applied to winding 22 of the same relay. Any disparity between the forces on thevrelay armature due to currents in the relay windings 2| and 22 calls for adjustment of they slope characteristic of equalizers 9 and 209, This adjustment is brought about by motor 24 which, in the event of disparity in the opposing forces and consequent movement of relay armature 23, adjusts contactar |9 to reduce the disparity. Simultaneously, it adjusts equalizers 9 and 209 to compensate for the indicated disparity between the slope characteristic of the preceding line section and the slope characteristic of the respective repeaters. Control motor 24 continues to operate until as a result of the movement of contactar I9 the relay armature is restored to a neutral position.

Automatic slope control for the opposite direction of transmission is'eiected by essentially the same method and means. Pilot waves f2 and f4 are picked off at the respective input ends of the corresponding sections of the repeater, and after rectification and amplification are applied to the control of differentialrelay 210, pilot f2 being operative in winding 212 thereof and pilot f4 being operative through voltage divider 268- by' the respective filters 269 in relay winding 21|. Relay 210 controls the operation of motor 214 which in turn controls the position of contactor 269 and simultaneously the slope characteristic introduced by the respective variable equalizers 259 and 59.

Whereas in Fig. 2 slope control for a given direction of transmission is effected by means of two pilots, such as fl and f3, that are transmitted in the same direction, it will be evident that oppositely directed pilots could be used for the same purpose in the manner shown in Fig. 1. That is, f I andf/Z could ble used in the manner shown in Fig. 1, and f3 and f4 could be likewise paired for control of slope in system No. 2. In the same way pilots fl and f4 could be paired for slope control in one system and f2 and f3 paired for slope control in the other system.

Whereas the invention has been described with reference to systems in which transmission vin both directions takes place over the same line circuit, the invention is not thus limited for it has application also to systems in which, for example,

vvariations in temperature are utilized for the respective directions of transmission.

What is claimed is:

1. A multiplex carrier wave transmission system comprising a transmission line subject to variations in attenuation, means for transmitting two sets of signals in respective frequency ranges in mutually opposite directions through said line, a multiplicity of two-way repeaters spaced apartin said line for amplifying said signals, means for transmitting an individual pilot wave concurrently with each of said sets of signals, means at each of said repeaters for separating the said two sets of signals -together with their individual pilot waves, an individual ampliiier for each separated set of signals and pilot wave, a flat gain regulator for each of said amplifiers controlled by the respectively corresponding pilot wave and operative to maintain said pilot wave at a substantially constant intensity at the output of the repeater, a slope regulator at one of said repeaters operative on one of said separatedsets of signals, means for conveying from another of said repeaters to said one repeater a measure of the amplitude of one of said pilot Waves as received at said other repeater after transmission from said one repeater, means at said one repeater for deriving a measure of the amplitude of the other of said pilot waves as received thereat after transmission from said other repeater, and means for automatically controlling said slope regulator in accordance with the disparity of said measures of amplitude.

2. A multiplex carrier wave transmission system comprising a transmission line subject to variations in attenuation, means for transmitting different sets of signals in different frequency ranges over said line from one terminal thereof to the other, means for transmitting concurrently with each of said sets of signals an individual pilot wave of non-signal frequency that is subject to substantially the same variations in attenuation as the said set of signals to which it is individual, means at a point along said line for separating and separately amplifying said diierent set of signals together with said respectively correspondingly pilot waves., a flat gain regulator for each of said separate amplifying means controlled by the respectively corresponding pilot wave, and a slope regulator operative on one of said sets of separated signals in accordance with the difference in attenuation experienced by said pilot waves in their transmission through said line. y

3. In a system for the transmission of signals in opposite directions in respective frequency ranges through a medium subject to variations in a propagation characteristic, the method which comprises transmitting control waves of different frequencies concurrently with the said signals in each direction of signal transmission, maintaining the intensity of both of said control waves substantially constant at widely separated points along said system, comparing the intensities of said control waves as received at said points after transmission through the intervening portion of said system, and automatically compensating said variations in said system in accordance with the relative intensities of said control waves as so compared.

4. In a two-way repeatered transmssion system, the method which comprises transmitting pilot currents of different frequencies in opposite directions through a repeater section and controlling -a transmission characteristic of a repeater at one end of said section in accordance with relative changes in a parameter of said pilot currents as received at opposite ends of said section.

5. In combination, a transmission line, a pair of terminal stations for said line comprising means for superposing a plurality of separate two-way multiplex signaling systems on said line, a repeater station along said line comprising means for separating the respective sets of signals of the several systems, Vand means for further separating the oppositely directed signals in each'of said separated sets, means for transmitting respective pilot waves in both directions of signal transmission for each of said superposed systems, an individual signal and pilot Wave ampliiier at said repeater station for each direction of transmission in each of said systems, means for `automatically regulating a transmission characteristic of each of said amplifiers under the separate control of the pilot wave individual thereto, and means for automatically regulating another transmission characteristic of at least one of said amplifiers under the joint control of a plurality of said pilot waves.

6. A combination in accordance with claim 5 in which said repeater station comprises means for deriving separate measures of the intensity of like-directed pilot waves as received at said repeater, a slope regulator for each of a plurality of said systems, and means for controlling said slope regulators in accordance with the relative values of the derived measures.

7. In a carrier transmission system, the method which comprises transmitting two pilot waves of diiferent frequencies over a line section, converting one of said pilot waves after transmission through the line section into a wave of different frequency, transmitting said wave of different frequency in the opposite direction through the same line section and utilizing it jointly with the other of said pilot waves to control the amplication of signals transmitted over a band of frequencies.

ESTILL I. GREEN. 

